It has been known for some time that cells, spores and the like, of microorganisms, which can be further propagated, tend to lose viability when dried, especially force dried e.g. by vacuum means. For commercial use of microorganisms, for example, as bioprotectants and herbicides and the like, dried material is the preferred item of commercial importance for both weight and handling considerations.
Trichoderma spp. are of increasing interest as bioprotectants against plant diseases (Harman and Lumsden, 1990, "The Rhizosphere" Lynch ed. pp.259-280, J. Wiley & Sons, NY; Harman et al., 1989, Plant Dis. 73:631-637; Papavizas, 1985, Phytopathology 74:1171-1175). Numerous papers have presented data on selection or production of strains for improved biocontrol efficacy (e.g. Hadar et al., 1984, Phytopathology 74:106-110; Sivan et al., 1987, Plant Dis. 71:587-592; Harman et al., 1989, supra; Stasz et al., 1988, Mycologia 80:141-150) and on delivery systems that provide effective biocontrol (Conway, 1986, Plant Dis. 70:835-839; Lewis et al., 1987, Plant Pathol. 36:438-446; Sivan et al., 1987, supra; Harman et al., 1989, supra). However, there is much less information on methods of producing large quantities of effective biomass as the active ingredient for microbial pesticides. Further, some work has relied upon semi-solid fermentation (Sivan et al., 1987, supra; Lewis et al., 1983, Soil Biol. Biochem. 15:351-357), which is of less interest to corporations wishing to market Trichoderma-based bioprotectants than is deep-tank fermentation.
Trichoderma spp. produces three kinds of propagules, i.e. hyphae, chlamydospores, and conidia (Papavizas, 1985, Ann. Rev. Phytopathol. 23:23-54). Biomass produced for biological control must retain a high level of viability after drying. Since hyphae do not withstand drying, hyphae biomass is not useful. Conidia are produced more abundantly than chlamydospores under optimal conditions; however, these optimal conditions usually include an aerial environment. Conidia are difficult to produce in submerged fermentation.
Some work published on production of Trichoderma biomass for biocontrol using liquid fermentation was directed toward production of chlamydospores, and required 10-21 days to produce optimal levels of biomass (Lewis et al., 1983, supra: Papavizas, et al., 1984, suora). Other work demonstrated that conidia could be produced rapidly under conditions of liquid fermentation, but did not investigate viability upon drying, or efficacy in biological control (Tabachaik, 1988, U.S. Pat. No. 4,837,155).
There are a number of requirements for biomass to be used for biological control, i.e. (1) biomass of appropriate spore composition must be produced in high levels rapidly, (2) the biomass must be able to withstand drying, (3) the dried material must have a high level of germinable, vigorous propagules, and (4) biomass should be of consistent quality from batch to batch.
This invention relates in part to the use of osmoticants to provide desiccation tolerance to growth producing cells of microorganisms upon drying and reconstitution.
This invention also relates in part to the discovery of liquid fermentation media permitting production of high levels of conidia of Trichoderma harzianum in liquid fermentation, and modifications to these media that produce conidia that are resistant to desiccation and that provide enhanced biocontrol efficacy.